1. Field of the Invention
The present invention relates to a small-sized load sensor unit which detects a magnitude of a load, and more particularly, to a small-sized load sensor unit which is small and lightweight and can be easily assembled to an apparatus, and which has excellent responsiveness to load variation and has high reliability by including a mechanism for preventing breakage of a part of detecting a load even when a load equal to or larger than a predetermined value is applied.
2. Description of the Related Art
JP-A-2002-54984 discloses a load sensor unit including a strain body deformed according to a magnitude of a load, a strain measuring unit, and a mechanism for restricting a displacement amount of the strain body according to the magnitude of the load such that the breakage of the strain body and the strain measuring unit can be prevented. For example, there is disclosed a scale which measures a load of an object placed on a tray. The scale includes a stopper mechanism which prevents deformation of a strain body when unexpected stress is applied to the strain body due to lifting of the tray, an excessive load or falling. Specifically, the scale includes a tray receiving plate which connects the strain body and the tray, a strain body holder which connects the strain body and a base portion, and a stopper mechanism in which a part of the tray receiving plate and a part of the strain body holder are fit thereto, and when a stress equal to or larger than a predetermined value is applied, the fit parts come into contact with each other, so that the strain body is not deformed further.
JP-A-2003-337053 discloses a flow sensor which measures a flow of a fluid. The flow sensor includes a displacement restricting member for diaphragms or a load difference sensor. When the load difference sensor detects a displacement due to variation in a fluid pressure on the diaphragms connected through an orifice, the displacement restricting member operates such that the displacement due to variation in the fluid pressure on the diaphragms does not become a predetermined amount or more.
That is, an apparatus and a strain body appropriate for an object to be measured or diaphragms and a manner of restricting the displacement amount of the strain body or the diaphragms may be designed at each time in performing weight measurement using a scale or flow measurement using a flow sensor, so that small-sized load sensor units each having an unique structure may be obtained. However, in this case, it takes a long time to evaluate a small-sized load sensor unit and an apparatus with the small-sized load sensor unit assembled therein. Therefore, it is difficult to develop an apparatus in a shorter time and implement earlier manufacture and sales. Also, it is burdensome to design a strain body according to a method of sensing a load and to spend a lot of time for experiments, evaluations, or the like at each time.
Further, if it is required to measure a load at high resolution or a minuscule differential pressure of a flow in detecting the displacement of a strain body or diaphragms by a strain measuring unit, it is necessary to improve the sensitivity of a sensor (strain measuring unit). That is, it is necessary to reduce the thickness of the strain body or diaphragms, thereby increasing a displacement amount, and to perform design change such as adjustment of a breakage preventing mechanism. Furthermore, there are burdens such as selection or design of a strain body according to a magnitude of a flow or a load, or a strain measuring unit according to the displacement amount of diaphragms.